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Microblaze 16×2 LCD DriverOn October 18, 2008, in Version 10.1, Xilinx Platform Studio (XPS), by Jeff

Tutorial Overview

In this example, we will develop a driver for the 16×2 character LCD on the ML505/6/7 board.The LCD driver will be mostly a Microblaze design, as opposed to being an IP design. Thephysical interface to the LCD will be made through a GPIO peripheral. The signal timingrequirements of the LCD will be achieved by using a Timer peripheral. The functions contained inthe software application will control what is shown on the LCD. The main function of thesoftware application will provide a simple example of how to clear the display, write a message onthe LCD and to change the cursor location.

The design is built on the interface specifications contained in the LCD datasheet. Theconnections to the FPGA are found on page 12 of the ML50x schematics. It is recommendedthat you read those documents before following this design.

This tutorial contains screenshots to guide you through the entire implementation process. Clickon the images to view a higher resolution.

Requirements

Before following this tutorial, you will need to do the following:

Buy an ML505/ML506/ML507 or XUPV5 board if you don’t already have one. Xilinx suppliesthe ML50x boards, but the best deal is the XUPV5 from Digilent. Click the Digilent link formore information.

Create the Basic Project

Follow these steps to create the basic project:

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1. Open XPS. From the dialog box, select “Base System Builder wizard” and OK.

2. You will be asked to specify which folder to place the project. Click “Browse” and create anew folder for the project. Click “OK”.

3. We are given the choice to create a new project or to create one using the template ofanother project. Tick “I would like to create a new design” and click “Next”.

4. On the “Select Board” page, select “Xilinx” as the board vendor. Select “Virtex 5 ML505Evaluation Platform” as the board name. Select “1″ as the board revision. Click “Next”.

5. On the “Select Processor” page, we normally have a choice between using the PowerPC“hard” processor, or the Microblaze “soft” processor. Since the Virtex-5 does not contain anyPowerPCs, we can only select Microblaze. Click “Next”.

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6. On the “Configure Microblaze” page, select the clock frequency to be 125MHz. For the BRAMlocal memory, select “64KB”. Select “No debug” and click “Next”.

7. In selecting the Additional IO Interfaces, leave “RS232_Uart_1″ ticked and un-tickeverything else.

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8. On the “Add Internal Peripherals” page, click “Next”.

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9. On the “Software Setup” page, select “RS232_Uart_1″ for both STDIN and STDOUT. Leave“Peripheral Test” ticked and un-tick “Memory Test”. Click “Next”.

10. Click “Generate”.

11. Click “Finish”.

Add the GPIO for the LCD

Now we will add a GPIO peripheral to allow the Microblaze to control the LCD.

1. In the IP Catalog tab, open the “General Purpose IO” tree.

2. Right click on “XPS General Purpose IO” and select “Add IP”.

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3. Connect the instance to the PLB bus by opening the “xps_gpio_0″ tree and selecting“mb_plb” for the “SPLB” bus connection.

4. Double click on the “xps_gpio_0″ instance. We can modify the instance parameters usingthis dialog box. Type “7″ for the “GPIO Data Channel Width” and click OK.

5. Select the “Ports” filter and open the “xps_gpio_0″ tree.

6. The “GPIO_IO” net should display “No Connection”. Click on “No Connection” and type“LCD_IO” to give the net a name.

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7. Click the net again to bring down the drop-down menu and select “Make External”. Thenewly created net should now be in the “External Ports” tree. XPS automatically modifies the“system.mhs” file to include the new external port.

8. Select the “Addresses” filter.

9. Click the “xps_gpio_0″ size drop-down menu and select 64K. Then click “GenerateAddresses”. XPS automatically reconfigures the memory map and gives the GPIO peripherala base address and a high address. It also automatically modifies the “system.mhs” file toupdate the IP address details.

We have now created an instance of the GPIO peripheral in our design. Later, we will modify theconstraints file to connect the GPIO peripheral IO port to the LCD.

Add the Timer Peripheral

We now add a timer peripheral to the project to allow the Microblaze to measure time delays. Adelay function will be used to create the required signal timing for the LCD interface. Followthese steps to add the peripheral:

1. In the IP Catalog tab, open the “DMA and Timer” tree.

2. Right click on “XPS Timer/Counter” and select “Add IP”.

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3. Connect the instance to the PLB bus by opening the “xps_timer_0″ tree and selecting“mb_plb” for the “SPLB” bus connection.

4. Select the “Addresses” filter.

5. Click the “xps_timer_0″ size drop-down menu and select 64K. Then click “GenerateAddresses”.

We have now created an instance of the Timer peripheral in our design.

Modify the Constraints (.UCF) File

The GPIO peripheral that we added to the design must be linked to the external pins on theFPGA that in turn connect to the LCD. The LCD interface consists of the 7 signals listed below.They are shown with pin description, pin name from the LCD datasheet, and the net name fromthe ML505 schematic. In brackets are the corresponding FPGA pins that they connect to on theML505 board.

Data bit 7, DB7, LCD_FPGA_DB7 (T11)

Data bit 6, DB6, LCD_FPGA_DB6 (G6)

Data bit 5, DB5, LCD_FPGA_DB5 (G7)

Data bit 4, DB4, LCD_FPGA_DB4 (T9)

Enable, E, LCD_FPGA_E (AC9)

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Read/Write, RW, LCD_FPGA_RW (AC10)

Register Select, RS, LCD_FPGA_RS (J17)

Follow these steps to add those pin locations to the constraints file:

1. Click the Project tab, open the “Project files” tree and double click the UCF file to open it.

2. Add the following lines of code to the end of the file:

#### Module LCD_IO constraints

# LCD_FPGA_DB4Net LCD_IO_pin<6> LOC = T9;Net LCD_IO_pin<6> IOSTANDARD=LVCMOS33;Net LCD_IO_pin<6> PULLDOWN;Net LCD_IO_pin<6> SLEW=SLOW;Net LCD_IO_pin<6> DRIVE=2;# LCD_FPGA_DB5Net LCD_IO_pin<5> LOC = G7;Net LCD_IO_pin<5> IOSTANDARD=LVCMOS33;Net LCD_IO_pin<5> PULLDOWN;Net LCD_IO_pin<5> SLEW=SLOW;Net LCD_IO_pin<5> DRIVE=2;# LCD_FPGA_DB6Net LCD_IO_pin<4> LOC = G6;Net LCD_IO_pin<4> IOSTANDARD=LVCMOS33;Net LCD_IO_pin<4> PULLDOWN;Net LCD_IO_pin<4> SLEW=SLOW;Net LCD_IO_pin<4> DRIVE=2;# LCD_FPGA_DB7Net LCD_IO_pin<3> LOC = T11;Net LCD_IO_pin<3> IOSTANDARD=LVCMOS33;Net LCD_IO_pin<3> PULLDOWN;Net LCD_IO_pin<3> SLEW=SLOW;Net LCD_IO_pin<3> DRIVE=2;# LCD_FPGA_RWNet LCD_IO_pin<2> LOC = AC10;Net LCD_IO_pin<2> IOSTANDARD=LVCMOS33;Net LCD_IO_pin<2> PULLDOWN;Net LCD_IO_pin<2> SLEW=SLOW;Net LCD_IO_pin<2> DRIVE=2;# LCD_FPGA_RSNet LCD_IO_pin<1> LOC = J17;Net LCD_IO_pin<1> IOSTANDARD=LVCMOS33;Net LCD_IO_pin<1> PULLDOWN;Net LCD_IO_pin<1> SLEW=SLOW;Net LCD_IO_pin<1> DRIVE=2;# LCD_FPGA_ENet LCD_IO_pin<0> LOC = AC9;Net LCD_IO_pin<0> IOSTANDARD=LVCMOS33;Net LCD_IO_pin<0> PULLDOWN;

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Net LCD_IO_pin<0> PULLDOWN;Net LCD_IO_pin<0> SLEW=SLOW;Net LCD_IO_pin<0> DRIVE=2;

Modify the Software Application

The software application controls the LCD interface signals by writing to the GPIO peripheral. Itcontains several functions for performing the signal sequences for writing characters to theLCD, moving the cursor, etc. To achieve the required signal timing, the application contains adelay function that uses the Timer peripheral.

1. From the “Applications” tab, open “Sources” within the “Project: TestApp_Peripheral” tree.Open the “TestApp_Peripheral.c” source file.

2. Replace all the code in this file with the following source and save the file.

#include "xparameters.h"#include "xbasic_types.h"#include "xgpio.h"#include "xstatus.h"#include "xtmrctr.h"

// Masks to the pins on the GPIO port

#define LCD_DB4 0x01#define LCD_DB5 0x02#define LCD_DB6 0x04#define LCD_DB7 0x08#define LCD_RW 0x10#define LCD_RS 0x20#define LCD_E 0x40#define LCD_TEST 0x80

// Global variables

XGpio GpioOutput;XTmrCtr DelayTimer;

// Function prototypes

void delay_us(Xuint32 time);void delay_ms(Xuint32 time);void gpio_write(Xuint32 c);Xuint32 gpio_read(void);void lcd_clk(void);void lcd_set_test(void);void lcd_reset_test(void);void lcd_set_rs(void);void lcd_reset_rs(void);void lcd_set_rw(void);void lcd_reset_rw(void);void lcd_write(Xuint32 c);void lcd_clear(void);void lcd_puts(const char * s);void lcd_putch(Xuint32 c);void lcd_goto(Xuint32 line,Xuint32 pos);void lcd_init(void);

// Main function

int main (void){ Xuint32 status;

// Clear the screen xil_printf("%c[2J",27); xil_printf("16x2 LCD Driver by Virtex-5 Resource\r\n"); xil_printf("http://www.fpgadeveloper.com\r\n");

// Initialize the Timer status = XTmrCtr_Initialize(&DelayTimer, XPAR_XPS_TIMER_0_DEVICE_ID); if (status != XST_SUCCESS){ xil_printf("Timer failed to initialize\r\n"); return XST_FAILURE; }

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XTmrCtr_SetOptions(&DelayTimer, 1, XTC_DOWN_COUNT_OPTION);

// Initialize the GPIO driver for the LCD status = XGpio_Initialize(&GpioOutput, XPAR_XPS_GPIO_0_DEVICE_ID); if (status != XST_SUCCESS){ xil_printf("GPIO failed to initialize\r\n"); return XST_FAILURE; } // Set the direction for all signals to be outputs XGpio_SetDataDirection(&GpioOutput, 1, 0x00);

// Initialize the LCD lcd_init();

// Example write to the LCD lcd_puts("http://www.fpga"); lcd_goto(1,2); lcd_puts("developer.com");

while(1){ }}

// Delay function (microseconds)void delay_us(Xuint32 time){ XTmrCtr_SetResetValue(&DelayTimer, 1, time * 125); XTmrCtr_Start(&DelayTimer, 1); while(!(XTmrCtr_IsExpired(&DelayTimer, 1))){} XTmrCtr_Stop(&DelayTimer, 1);}

// Delay function (milliseconds)void delay_ms(Xuint32 time){ XTmrCtr_SetResetValue(&DelayTimer, 1, time * 125000); XTmrCtr_Start(&DelayTimer, 1); while(!(XTmrCtr_IsExpired(&DelayTimer, 1))){} XTmrCtr_Stop(&DelayTimer, 1);}

// Write to GPIO outputsvoid gpio_write(Xuint32 c){ // Write to the GP IOs XGpio_DiscreteWrite(&GpioOutput, 1, c & 0x0FF);}

// Read the GPIO outputsXuint32 gpio_read(){ // Read from the GP IOs return(XGpio_DiscreteRead(&GpioOutput, 1));}

// Clock the LCD (toggles E)void lcd_clk(){ Xuint32 c; // Get existing outputs c = gpio_read(); delay_us(1); // Assert clock signal gpio_write(c | LCD_E); delay_us(1); // Deassert the clock signal gpio_write(c & (~LCD_E)); delay_us(1);}

// Assert the RS signalvoid lcd_set_rs(){ Xuint32 c;

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// Get existing outputs c = gpio_read(); // Assert RS gpio_write(c | LCD_RS); delay_us(1);}

// Deassert the RS signalvoid lcd_reset_rs(){ Xuint32 c; // Get existing outputs c = gpio_read(); // Assert RS gpio_write(c & (~LCD_RS)); delay_us(1);}

// Assert the RW signalvoid lcd_set_rw(){ Xuint32 c; // Get existing outputs c = gpio_read(); // Assert RS gpio_write(c | LCD_RW); delay_us(1);}

// Deassert the RW signalvoid lcd_reset_rw(){ Xuint32 c; // Get existing outputs c = gpio_read(); // Assert RS gpio_write(c & (~LCD_RW)); delay_us(1);}

// Write a byte to LCD (4 bit mode)void lcd_write(Xuint32 c){ Xuint32 temp; // Get existing outputs temp = gpio_read(); temp = temp & 0xF0; // Set the high nibble temp = temp | ((c >> 4) & 0x0F); gpio_write(temp); // Clock lcd_clk(); // Delay for "Write data into internal RAM 43us" delay_us(100); // Set the low nibble temp = temp & 0xF0; temp = temp | (c & 0x0F); gpio_write(temp); // Clock lcd_clk(); // Delay for "Write data into internal RAM 43us" delay_us(100);}

// Clear LCDvoid lcd_clear(void){ lcd_reset_rs(); // Clear LCD lcd_write(0x01); // Delay for "Clear display 1.53ms" delay_ms(2);}

// Write a string to the LCD

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void lcd_puts(const char * s){ lcd_set_rs(); while(*s) lcd_write(*s++);}

// Write character to the LCDvoid lcd_putch(Xuint32 c){ lcd_set_rs(); lcd_write(c);}

// Change cursor position// (line = 0 or 1, pos = 0 to 15)void lcd_goto(Xuint32 line, Xuint32 pos){ lcd_reset_rs(); pos = pos & 0x3F; if(line == 0) lcd_write(0x80 | pos); else lcd_write(0xC0 | pos);}

// Initialize the LCDvoid lcd_init(void){ Xuint32 temp;

// Write mode (always) lcd_reset_rw(); // Write control bytes lcd_reset_rs();

// Delay 15ms delay_ms(15);

// Initialize temp = gpio_read(); temp = temp | LCD_DB5; gpio_write(temp); lcd_clk(); lcd_clk(); lcd_clk();

// Delay 15ms delay_ms(15);

// Function Set: 4 bit mode, 1/16 duty, 5x8 font, 2 lines lcd_write(0x28); // Display ON/OFF Control: ON lcd_write(0x0C); // Entry Mode Set: Increment (cursor moves forward) lcd_write(0x06);

// Clear the display lcd_clear();}1. Right click on “Project: TestApp_Peripheral” and click “Generate Linker Script”.

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2. Click “OK” to generate the linker script.

Download and Test the Project

1. Open a Hyperterminal window with the required settings. For the correct settings, seeHyperterminal Settings.

2. Turn on the ML505 board.

3. From the EDK, select “Device Configuration->Download Bitstream”.

The software application simply initializes the LCD, clears the display and writes a message overthe two lines. The LCD should look as shown in the image below.

You can download the project files for this tutorial and try it on your ML50x board. Please selectthe file corresponding to your board, right-click on it and select “Save Link As”. You can alsodownload the project files here on GitHub.

Board Virtex-5 Version Project filesML505 XC5VLX50T LCDDriver-ML505-EDK10-1.zipML506 XC5VSX50T LCDDriver-ML506-EDK10-1.zipML507 XC5VFX70T LCDDriver-ML507-EDK10-1.zipXUPV5 XC5VLX110T LCDDriver-ML509-EDK10-1.zip

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